A plastic container for preserving and distributing foods by sealing them into the container and subjecting them to sterilization treatment at a high temperature is on the increase. Also, in some cases, consumers heat the same by means of a microwave oven in their use, and when the contents contain an oil, the temperature of the contents become high in some cases, so that it has been desired as the consumers' needs that the heat resistance and sealability in the cooking is excellent and, in addition, the openability is excellent. As a container excellent in sealability and easy openability, many proposals have been made for containers in which both sealability and easy openability have been attained by using a multilayer container and using the interface between layers of the multilayer container as an opening peel plane, without effecting the opening at the time of use by peeling the sealed portion which is generally effected (JP-A-50-37,598, JP-B-5-63,385 and JP-B-5-79,587). However, in these containers, the peeling layer is made of PE (polyethylene), and hence, they are disadvantageous in that 120.degree. C. is the upper limit as a high temperature treating condition; that particularly when they are filled with cooked foods containing a large amount of oils, swelling is seen in the peeling layer; that the seal with a lid material is broken because of the softening of the seal layer due to the high temperature; and the like.
For the purpose of overcoming these disadvantages, there is proposed a container having such a layer construction that a polypropylene resin is used as the innermost layer to increase the heat resistance as disclosed in JP-B-7-2,409, whereby the heat resistance has been enhanced as compared with the conventional container having a PE innermost layer. In such a construction, however, PE is still used as an intermediate layer for making peeling possible, and hence, the enhancement of heat resistance to some extent is found but there is such a disadvantage that since in the case of sterilization at a higher temperature (e.g., 130.degree. C.) the intermediate layer is softened and melted, the laminate strength between the intermediate layer and the surface layer is rapidly lowered and peel is caused during the sterilization and therefore the sealability is impaired. In addition, for the overall heat resistance of the container, it is necessary to use a material superior in heat resistance because the use of a usual PP results in a distortion.
The object of this invention is to provide a laminate which is suitably used in the production of an easily openable container in which the heat seal layer and the opening peel layer are made different, and which has heat resistance and oil resistance while keeping easy peelability of the opening peel layer.